CHP Radiation Shielding Design and Analysis 2

Question 1

NCRP Report No. 151 provides shielding guidance for medical X-ray facilities. The concept of 'workload' (W) is defined as:

Accepted Answer

The weekly time-integrated tube current expressed in mA·min/week

Answer

The total number of patients imaged per week

Answer

The peak kilovoltage setting of the X-ray tube

Answer

The occupancy factor of the area to be shielded

Question 2

In NCRP 151 shielding calculations for diagnostic X-ray rooms, the 'use factor' (U) accounts for:

Accepted Answer

The fraction of the workload during which the primary beam is directed at a given wall

Answer

The fraction of time the room is occupied by non-radiation workers

Answer

The efficiency of the shielding material at the relevant photon energy

Answer

The fraction of total patients requiring repeat exposures

Question 3

For a point isotropic gamma source in air, if the distance from the source doubles, the dose rate changes by a factor of:

Accepted Answer

Decreases by factor of 4

Answer

Decreases by factor of 2

Answer

Increases by factor of 4

Answer

Decreases by factor of 8

Question 4

Concrete is commonly used for gamma and neutron shielding in nuclear facilities primarily because:

Accepted Answer

It provides both gamma attenuation (high density) and neutron moderation (hydrogen content) in a structural material

Answer

It has a high Z number comparable to lead, maximizing photoelectric attenuation

Answer

It eliminates secondary gamma production from neutron capture reactions

Answer

It has the lowest cost per HVL among all shielding materials

Question 5

The linear attenuation coefficient (μ) for photons in a material has units of:

Accepted Answer

cm⁻¹

Answer

cm²/g

Answer

g/cm²

Answer

MeV⁻¹

Question 6

When designing shielding for a PET facility, which photon energy must the shielding primarily address?

Accepted Answer

511 keV (annihilation photons from positron emission)

Answer

140 keV (from Tc-99m)

Answer

1.274 MeV (from Na-22 gamma decay)

Answer

364 keV (from I-131 gamma emission)

Question 7

In reactor shielding design, 'skyshine' refers to:

Accepted Answer

Radiation that travels upward, scatters in the atmosphere, and returns to ground level at a distance from the facility

Answer

Neutron activation of atmospheric nitrogen above the reactor

Answer

Reflected gamma radiation from the reactor building roof

Answer

Direct streaming through ventilation ducts in the reactor building